Comparative studies of the effects of recombinant GM-CSF and GM-CSF administered via a poxvirus to enhance the concentration of antigen-presenting cells in regional lymph nodes

Repeated subcutaneous (s.c.) injections of recombinant granulocyte-macropha ge colony-stimulating factor (recGM-CSF) for 4-5 days can enrich an immuniz ation site with antigen-presenting cells (APC), which has been correlated w ith improved immune responses in experimental and clinical studies. A recom binant vaccinia virus encoding the GM-CSF gene (rV-GM-CSF) has been develop ed and can generate specific antitumour immunity in a whole tumour cell vac cine. In the present study, we examined whether rV-GM-CSF could produce and release GM-CSF locally which, in turn, might enrich a site of immunization for APC as preciously shown for recGM-CSF. S.c. injection of rV-GM-CSF sig nificantly (P < 0.05) enhanced the percentage and overall number of APC, me asured by class II expression levels, in the regional lymph nodes that drai n the injection site. Dose- and temporal-dependent studies showed class II expression levels in the draining lymph nodes were maximally enhanced 5-7 d ays after a single injection of 10(7) plaque-forming units (pfu) of rV-GM-C SF. Flow cytometry revealed that the increase in class II expression result ed from (i) a higher class II expression level on CD19(+) B cells and (ii) an increase in the number of CD11c(+)/class II+ professional APC within the draining lymph nodes. Moreover, isolation of lymph nodes from rV-GM-CSF-tr eated mice revealed their capacity to support higher levels of antigen-spec ific T cell proliferation and allospecific cytotoxic responses. A compariso n between a single injection of rV-GM-CSF and a 4-day course of recGM-CSF r evealed comparable changes in class II expression and functional T cell ass ays. GM-CSF can be delivered in a recombinant poxvirus, and the local produ ction of the cytokine results in cellular and phenotypic changes that are s imilar to those of recGM-CSF. The ability to utilize rV-GM-CSF as a single inoculum may be more compatible with traditional immunization strategies. ( C) 2000 Academic Press.